I get from that article that they are at a loss to explain how it could have happened, but the amount if tiny enough that they have decided not to worry about it. Xenon 134 was what was detected. It has a half life of 9 hours or so, which means it can't be a by-product from some time ago, it had to be very recent. No alarm bells yet from any experts not connected with the gov't so I hope that is a good sign.

Yeah, now it is being acknowledged by TEPCO for the first time that small scale re-criticalities (love this terminology that flies off my fingers so easily now...) have probably occurred any number of times. Many experts not affiliated with the plant have been saying this since the beginning.

Here are some meaty blurbs from an article I just read:

"The presence of xenon 135 in particular, which has a half-life of just nine hours, seemed to indicate that fission took place very recently."

"The government censured the Nuclear and Industrial Safety Agency, for failing to report the discovery to the prime minister’s office for hours."

"The developments added to the disquiet over handling of information related to the disaster. For almost two months after the March 11 earthquake and tsunami, disaster, both company and government officials declared it was unlikely any meltdown had occurred at all at the Fukushima Daichi nuclear complex, finally conceding that the fuel had indeed slumped and had likely breached containments in three reactors."

"But even in their most dire assessments, some experts had not expected even bursts of re-criticality to occur, because it was unlikely that the fuel would melt in just the right way — and that another ingredient, water, would be present in just the right amounts — to allow for any nuclear reaction. If episodes of fission at Fukushima were confirmed, an expert confided, “our entire understanding of nuclear safety would be turned on its head.”

"A former nuclear engineer with three decades of experience at a major engineering firm, meanwhile, said that sustained re-criticality remained highly unlikely. But his main concern was that officials could not pinpoint the exact location of the nuclear fuel — which would greatly complicate the cleanup."

TEPCO released a statement a number of days ago that concluded that the particles detected were not due to any criticality, but other short term phenomenon, because even a very short criticality would have resulted in tens of thousands the amount of xenon as was detected. I have seen no scientists disputing this conclusion.

Even with this, I am still seeing "weekend update" English news that is repeating the same worrisome criticality reports. I guess that is just more interesting than "it's probably nothing." I'll take the boring version of this news any day of the week.

The Tokyo Electric Power Company in Japan plans to revise its criteria for determining if a damaged nuclear power plant is poised to start a dangerous, "critical" chain reaction of fission.

The revisions come in the wake of confusion over whether the damaged Fukushima Daiichi nuclear plant had gone critical, generating neutrons through the fission, or splitting, of uranium nuclei that would then go on to split more nuclei in a runaway process.

On 1 November, TEPCO announced it had detected worryingly high levels of radioactive xenon, a by-product of fission, near the plant's Number 2 reactor. This prompted anxious headlines around the world.

But it was a false alarm. The xenon came from the natural radioactive decay, or "spontaneous" fission, of the element curium, a product of a working nuclear reactor. Curium can turn into xenon via two pathways, either directly or by first decaying into radioactive iodine, which then decays into xenon. TEPCO had only considered the first pathway, says physicist Ron Fleming at the University of Michigan in Ann Arbor.

"It seems like the scientists are completely caught off guard and improvising as they go along," says physicist Ferenc Dalnoki-Veress at the James Martin Center for Nonproliferation Studies in Monterey, California.

----Completely off guard and improvising... These are not words I want to hear. I never had a really strong feeling one way or the other about nuke power; I am indisputably against it now.

This is likely the longest I have gone without an "update". Very likely because I too am finally getting used to the status quo.

TEPCO again finally admitted that at least reactor no. 1 was a full meltdown, but still claims it thinks that 1/4 of the concrete barrier beneath it's containment is still intact. I, among others, am dubious. I wouldn't even make bets on the other two reactors "breach" level.link, if you like

The man who has been in charge of the plant since 2008, and oversaw the plant up until today, Yoshida, is stepping down due to health reasons after a routine checkup. It seems heavy, but all insist it is not related to the 9 month meltdown combat operation. He is considered a hero by many, including myself. He and a suicide crew stuck it out when many would have bolted. The gov't and TEPCO at one point quite early in the crisis became concerned from a flawed advisory that seawater could raise risk of a recriticality and ordered Yoshida to stop seawater injection. It was eventually confirmed that Yoshida had ignored these direct orders without telling TEPCO and the gov't for fear of being removed and the injection being stopped. He continued the injection, for which he was later reprimanded. It is the general opinion now that this decision mitigated a worse crisis.

More and more rice harvests around the region surrounding the plant are coming up too high for consumption. Worries are increasing about how far this will go. A new analysis of weather patterns during the crisis postulates that most of the rest of Japan (western Honshu and Shikoku) likely got a peppering of radiation. This means food supplies should be tested there as well, but I have neither seen nor heard of any testing. We are having our rice (the wife does most of the cooking and she's Japanese) sent from Kyushu. This is the southernmost of Japan's 4 main islands, and is as safe as we can get domestically. There is no foreign rice in Japan as far as I know; this situation may change if things start to look worse.

On a more personal note, I have mentioned that the area just outside of Tokyo that I work in has higher radiation readings than the rest of Tokyo. A man in the office where I work takes one of those expensive handheld radiation detectors out every day and measures radiation in 4 or 5 areas. He told me where they are posting the data (not online or I might've linked it.) I don't like the numbers. They wouldn't have been considered "safe" 10 months ago. Not much I can do. It is the most secure, well-paying job I have had here. I just feel lucky that I am an adult and at much less risk than all the kids living in the area. People don't seem worried though. They continue to trust the government. The latest projections, foreign and domestic, do say (at this point at least) that it will probably be very difficult to identify any kind of "spike" in cancer numbers in the years to come. All eyes will especially be on thyroid cancers in people who were kids in the general area during the worst of this. I pray pray for the future.

Our apartment complex was sold, and a routine inspection seems to have confirmed that our building is no longer up to new earthquake standards and they are asking everyone to make plans to move out. We are negotiating the terms of our "withdrawal". I was always planning to use such an opportunity to move closer to my work, but now it doesn't seem such a bad thing having to travel over an hour to work every day. It's okay though. My wife just secured a really good job right here, and I get a lot of work done during my commute - making my coworkers scratch their heads at how I never seem to have much deskwork to do.

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